A number of orthodontic assemblies for correcting the alignment of teeth for aesthetic or functional deficiencies are known. Generally, such assemblies are attached to individual teeth and provide a bracket for an archwire. One type of bracket assembly is attached to teeth by a band which circles the tooth and has the bracket on the outside of the tooth. A second, more recent, type of assembly has a bonding pad which is attached to a tooth by an adhesive. Typically, this type of assembly has a base for attachment to a bonding pad on the tooth. Attached to the base are two tie wings having a generally T-shaped cross section which are attached to the base at the bottom of the "T". The tie wings are typically attached to the base in a parallel orientation and have cross-wise slots for placement of an archwire.
In use, a number of such brackets are attached to individual teeth. An archwire is fitted into the cross-wide slots and fixed in position using the wire ends. The archwire provides a desired directional force which is transmitted through the brackets to the teeth for realigning the teeth.
Previously, such brackets were generally rectangular in shape and the cross-wise slot was disposed at right angles to the sides of the tie wings. With such brackets, however, the archwire had to be bent in between the brackets to obtain the desired tooth realigning pressure. This method of use presented problems when replacing the archwire because reproduction of the bending in the archwire was difficult and caused difficulties with obtaining a continuous uniform force on teeth.
This difficulty was addressed by Andrews in U.S. Pat. No. 3,477,128. Andrews discloses that the cross-wise slots in orthodontic brackets could be cut at non-right angles with respect to the sides of the bracket assembly. In this manner, an unbent or "passive" archwire can be used to impart the necessary realigning force to teeth.
This type of apparatus, however, presented two problems: (1) inaccurate alignment of the bracket on the tooth and (2) weakened tie wings. Each tooth has a preferred angle between the long axis of the tooth and the occlusal plane of the mouth. In the general method of realigning teeth using orthodontic brackets, the cross-wise slot is aligned parallel to the occlusal surface of a patient's tooth. As a realigning pressure is applied to the tooth, the occlusal surface of the tooth is moved into alignment with the occlusal plane of the mouth. If an angled cross-wise slot is provided in a bracket having an otherwise rectangular outline, the only reference line for positioning the cross-wise slot parallel to the occlusal plane of the tooth is the slot itself. Such brackets are difficult to position easily and quickly on a patient's tooth.
The other problem presented by the use of angled cross-wise slots is weakening of portions of the tie wings. If two aligned angled cross-wise slots are provided through a pair of the wings on a bracket assembly having a rectangular outline, the cross slot in each tie wing will be located off center on the tie wing. Such tie wings have portions of the tie wing above and below the cross-wise slot having different thicknesses or amounts of tie wing material, and therefore, are of different strengths. As a force is produced by the archwire and transmitted through the bracket to the tooth, the weaker end of each tie wing is more likely to become damaged by the archwire force.
In U.S. Pat. No. 4,415,330, to Daisley, these problems were addressed by an orthodontic bracket design. The orthodontic bracket assembly in Daisley has a pair of tie wings which form a rhomboidal configuration having archwire slots which bisect the tie wings so that the tie wing tips on either side of the slot are of equal size. In this manner, planes formed by the tops and bottoms of the tie wings are parallel with the archwire slot and can be used for alignment with the occlusal surface of a patient's tooth. Also, because the tie wings are bisected by the archwire slots, the portions of the tie wing above and below the slot are of equal size and equal strength. Because the tie wings have a rhomboidal configuration, the tips of the tie wings have angular outside corners and flat top and bottom surfaces.
A line of orthodontic bracket assemblies, which is currently commercially available and identified by the trademark "The Master Series", is based on U.S. Pat. No. 4,415,330. The brackets of these assemblies have a rhomboidal configuration and are manufactured using a machining process rather than a molding or casting process.
FIGS. 6 and 7 in U.S. Pat. No. 4,415,330, which are designated as "prior art", illustrate two types of orthodontic brackets for use with a passive archwire. These brackets do not satisfactorily address or solve problems relating to alignment with the occlusal plane and weakened tie wing tips due to angled cross-wise slots. The tie wings of these bracket assemblies have angular corners on the tips. These two types of brackets are also known to be made by a machining process, rather than by a molding or casting process.
Another orthodontic bracket assembly currently available is identified by the trademark "SinterLine." Such bracket assemblies have a pair of tie wings having curved outside edges on the tie wings and substantially rounded wing tips. These brackets are designed for improved aesthetic appearance as well as increased patient comfort due to a smoother rounded apparatus. The SinterLine orthodontic brackets are manufactured by a method of casting or molding. The assemblies manufactured by such processes are generally relatively more expensive than those produced by machining techniques, particularly in the case in which a workable machining capability is already available.
Although many differently configured orthodontic brackets have been utilized, it would still be advantageous to provide a relatively inexpensive bracket that is acceptable to the orthodontic practitioner and is also comfortable for the wearer. Accordingly, it is an object of the present invention to provide an orthodontic bracket assembly having a smooth rounded configuration for increased patient comfort which is manufactured by a machining process, rather than a casting or molding process. It is a further objective of the invention to provide an orthodontic bracket assembly which has multiple references for alignment and which has archwire slots bisecting the tie wings.